The wireless local-area network (WLAN) technology known as “Wi-Fi” has been standardized by IEEE in the 802.11 series of specifications (i.e., as “IEEE Standard for Information technology—Telecommunications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”). As currently specified, Wi-Fi systems are primarily operated in the 2.4 GHz or 5 GHz bands.
The IEEE 802.11 specifications regulate the functions and operations of the Wi-Fi access points or wireless terminals, collectively known as “stations” or “STA,” in the IEEE 802.11, including the physical layer protocols, Medium Access Control (MAC) layer protocols, and other aspects needed to secure compatibility and inter-operability between access points and portable terminals. Because Wi-Fi is generally operated in unlicensed bands, communication over Wi-Fi may be subject to interference sources from any number of both known and unknown devices. Wi-Fi is commonly used as wireless extensions to fixed broadband access, e.g., in domestic environments and in so-called hotspots, like airports, train stations and restaurants.
Recently, Wi-Fi has been subject to increased interest from cellular network operators, who are studying the possibility of using Wi-Fi for purposes beyond its conventional role as an extension to fixed broadband access. These operators are responding to the ever-increasing market demands for wireless bandwidth, and are interested in using Wi-Fi technology as an extension of, or alternative to, cellular radio access network technologies. Cellular operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3rd-Generation Partnership Project (3GPP), including the radio-access technologies known as Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and Global System for Mobile Communications (GSM), see Wi-Fi as a wireless technology that can provide good additional support for users in their regular cellular networks.
Many of today's portable wireless devices (referred to hereinafter as “user equipments”, “UEs”, or more generally “terminal devices”) support Wi-Fi in addition to one or several 3GPP cellular technologies. In many cases, however, these terminal devices essentially behave as two separate devices, from a radio access perspective. The 3GPP-specified radio access network (RAN) and the UE-based modems and protocols that are operating pursuant to the 3GPP specifications are generally unaware of the wireless access Wi-Fi protocols and modems that may be simultaneously operating pursuant to the 802.11 specifications. Techniques for coordinated control of these multiple radio-access technologies are needed.
It is currently discussed in 3GPP how 3GPP Radio Access Technologies (RATs) can be integrated and/or interwork with WLAN. The focus of this work is how to perform access selection and/or traffic steering or routing between 3GPP and WLAN. One possible way in which access network selection and/or traffic steering or routing can be performed between two RATs is presented below.
In this technique the 3GPP network sends a set of conditions and/or thresholds to the UE which are used by the UE in one or more pre-defined rules dictating when the UE should steer traffic from one RAT to the other.
For example, a pre-defined rule could be as shown in Table 1, where values for threshold1, threshold2, threshold3 and threshold4 are provided to the UE by the 3GPP network i.e. a network node of the 3GPP RAT, such as an eNodeB, NodeB or radio network controller (RNC).
TABLE 1if (3GPP signal < threshold1) && (WLAN signal > threshold2) {  steerTrafficToWLAN( );} else if (3GPP signal > threshold3) || (WLAN signal < threshold4) {  steerTrafficTo3gpp( );}
Thus, according to this rule, if the UE-measured 3GPP signal is below threshold1 and the UE-measured WLAN signal is above threshold2, then the UE steers traffic to WLAN. Otherwise, if the 3GPP signal is above threshold3 or the WLAN signal is below threshold4, the UE steers traffic to the 3GPP network.
The term ‘3GPP signal’ herein could mean the signal transmitted by a radio network node belonging to a 3GPP RAT, e.g. a node in a LTE, HSPA, GSM etc. network, and/or it could be the quality of such a signal. The term WLAN signal′ herein could mean the signal transmitted by a radio network node belonging to WLAN, e.g. an access point (AP) etc., and/or it could be the quality of such a signal. Examples of measurements of 3GPP signals include reference signal received power (RSRP) and reference signal received quality (RSRQ) in LTE or common pilot channel (CPICH) received signal code power (RSCP) and CPICH Ec/No in HSPA. Examples of measurements of WLAN signals are Received Signal Strength Indicator (RSSI), Received Channel Power Indicator (RCPI), Received Signal to Noise Indicator (RSNI), etc.
With the above mobility mechanism, it is likely that the 3GPP network operator would like to restrict the WLANs that are considered by the terminal device in evaluating the rule. For example, the operator of the 3GPP network may wish to restrict the terminal device to only those WLANs that belong to the 3GPP network operator. Thus, there is a need for the 3GPP network to indicate to the terminal device which WLANs should be considered by the terminal device during the access network selection and/or traffic steering or routing procedure.
Different mechanisms have been proposed for this which are based on either the dedicated signalling of the WLAN identifiers to the terminal devices or on the broadcasting of WLAN identifiers to terminal devices.
Transmission of WLAN identifiers to a terminal device using dedicated signalling has the benefit of avoiding overhead in the broadcast channel, but dedicated signalling would require the network to signal the WLAN identifiers separately to each terminal device. This could introduce some network and terminal complexity, and depending on the scenario, dedicated signalling may result in a lot of signalling load in a dedicated signalling channel.
The broadcast of the WLAN identifiers in a broadcast channel also has some limitations, e.g. with respect to broadcast channel load. It may not be feasible, or even possible, to signal multiple WLAN identifiers during a single transmission in a broadcast channel.
Thus, there is a need for an improved technique for providing a list of WLAN identifiers to a terminal device for use in an access network selection and/or traffic steering or routing procedure.